• 한국자기학회:학술대회 개요집
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• 한국자기학회 2003년도 하계학술연구발표회 및 한.일 공동심포지엄
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• pp.220-221
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• 2003

Equiatomic FePt and CoPt alloy thin films have received considerable attention as possible magnetic and magneto-optic recording because of their high magnetic anisotropy energy and high coercivity. The high coercivity in these thin films is due to the presence of finely dispersed ordered FePt phase mixed with disordered FePt phase. However, a high temperature treatment, either substrate heating during deposition or post annealing, is needed to obtain the ordered L1$\_$0/ phase with high value of magneto crystalline anisotropy. Recent microstructural studies on these films suggest that the average grain size ranges from 10-50 nm and the grains are magnetically coupled between each other. On the other hand, the ultrahigh-density magnetic recording media with low media noise imposes the need of a material, which consists of magnetically isolated grains with size below 10 nm. The magnetic grain isolation can be controlled by the amount of additional non-magnetic element in the system which determines the interparticle separation and therefore the interparticle interactions. Recently, much research work has been done on various non-magnetic matrices. Preliminary studies showed that the samples prepared in B$_2$O$_3$ and Carbon matrices have shown strong perpendicular anisotropy and fine grain size down to 4nm, which suggest these nanocomposite films are very promising and may lead to the realization of a magnetic medium capable of recording densities beyond 1 Tb/in$^2$. So, in this work, the effect of Carbon doping on the magnetic properties of FePt nanoparticles were investigated.

• 한국정밀공학회지
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• 제23권9호
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• pp.54-60
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• 2006

Fitting process carried out in automobile transmission assembly line is classified into three classes; heat fitting, press fitting, and their combined fitting. Heat fitting is a method that heats gear to a suitable range under the tempering temperature and squeezes it toward the outer diameter of shaft. Its stress depends on the yield strength of gear. Press fitting is a method that generally squeezes gear toward that of shaft at room temperature by press. Another method heats warmly gear and safely squeezes it toward that of shaft. Warm shrink fitting process for automobile transmission part is now gradually increased, but the parts (shaft/gear) assembled by this process produced dimensional changes of gear profile in both radial and circumferential directions. So that it may cause noise and vibration between gears. In order to solve these problems, we need an analysis of warm shrink fitting process, in which design parameters are involved; contact pressure according to fitting interference between outer diameter of shaft and inner diameter of gear, fitting temperature, and profile tolerance of gear. In this study, an closed form equation to predict contact pressure and fitting load was proposed in order to develop optimization technique of warm shrink fitting process and verified its reliability through the experimental results measured in the field and FEM, that is, thermal-structural coupled field analysis. Actual loads measured in the field have a good agreement with the results obtained by theoretical and finite element analysis and also the expanded amounts of the gear profile in both radial and circumferential directions are within the limit tolerances used in the field.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2008년도 International Symposium on Remote Sensing
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• pp.441-444
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• 2008

This paper describes the development of a circularly polarized microstrip antenna, as a part of the Circularly Polarized Synthetic Aperture Radar (CP-SAR) sensor which is currently under developed at the Microwave Remote Sensing Laboratory (MRSL) in Chiba University. CP-SAR is a new type of sensor developed for the purpose of remote sensing. With this sensor, lower-noise data/image will be obtained due to the absence of depolarization problems from propagation encounter in linearly polarized synthetic aperture radar. As well the data/images obtained will be investigated as the Axial Ratio Image (ARI), which is a new data that hopefully will reveal unique various backscattering characteristics. The sensor will be mounted on an Unmanned Aerial Vehicle (UAV) which will be aimed for fundamental research and applications. The microstrip antenna works in the frequency of 1.27 GHz (L-Band). The microstrip antenna utilized the proximity-coupled method of feeding. Initially, the optimization process of the single patch antenna design involving modifying the microstrip line feed to yield a high gain (above 5 dBi) and low return loss (below -10 dB). A minimum of 10 MHz bandwidth is targeted at below 3 dB of Axial Ratio for the circularly polarized antenna. A planar array from the single patch is formed next. Consideration for the array design is the beam radiation pattern in the azimuth and elevation plane which is specified based on the electrical and mechanical constraints of the UAV CP-SAR system. This research will contribute in the field of radar for remote sensing technology. The potential application is for landcover, disaster monitoring, snow cover, and oceanography mapping.

• Progress in Superconductivity
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• 제13권3호
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• pp.139-145
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• 2012

Electric activity of cardiac muscles generates magnetic fields. Magnetocardiography (or MCG) technology, measuring these magnetic signals, can provide useful information for the diagnosis of heart diseases. It is already about 40 years ago that the first measurement of MCG signals was done by D. Cohen using SQUID (superconducting quantum interference device) sensor inside a magnetically shielded room. In the early period of MCG history, bulky point-contact RF-SQUID was used as the magnetic sensor. Thanks to the development of Nb-based Josephson junction technology in mid 1980s and new design of tightly-coupled DC-SQUID, low-noise SQUID sensors could be developed in late 1980s. In around 1990, several groups developed multi-channel MCG systems and started clinical study. However, it is quite recent years that the true usefulness of MCG was verified in clinical practice, for example, in the diagnosis of coronary artery disease. For the practical MCG system, technical elements of MCG system should be optimized in terms of performance, fabrication cost and operation cost. In this review, development history, technical issue, and future development direction of MCG technology are described.

• 한국ITS학회 논문지
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• 제4권2호
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• pp.81-87
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• 2005

본 논문에서는 도플러 레이더 시스템의 신호원이 되는 전압제어 발진기를 설계 및 제작하였다. 제안된 VCDRO는 CPW라인 형태를 이용하여 동조시키는 새로운 방법을 이용하였다. 유전체 공진기 기판 됫면에 바랙터 다이오드가 실장된 $\lambda$_{g}$/2 길이를 갖는 CPW 회로를 구현하여 유전체공진기와 커플링을 시켰다. 바랙터 다이오드는 CPW 한쪽 끝에 실장을 하였다. 제안된 CPW 동조회로는 여러 개의 다이오드를 실장 할 수 있어 동조대역폭을 쉽게 늘일 수 있다. 동조된 전압제어 발진기는 바랙터 다이오드의 전압을 0$\~$15V 로 가변시 12MHz 의 동조대역폭을 나타내었다. 제안된 CPW라인으로 동조된 위상고정 유전체 발진기는 10.5250Hz에서16.5dBm의 출력을 나타내었으며, 위상잡음은 -l15dBc/Hz@100kHz,-105dBcHz@10kHz,-102dBc/@1kHz 의 위상잡음 특성을 나타내었다.

• 대한기계학회논문집A
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• 제41권10호
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• pp.915-921
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• 2017

최근 자동차의 진동과 소음을 줄이기 위한 연구가 활발하게 이루어지고 있으나 기존의 연구들은 수동형 또는 능동형 마운트를 포함한 마운팅 시스템의 최적화에 대해서는 주목하지 않았다. 본 연구는 진동 소음원과 리시버 사이에 세 개의 구조적 경로를 가진 능동 마운팅 시스템에 대한 분석적인 연구를 수행하며 실제 시스템에의 적용 가능성을 확인한다. 능동 마운팅 시스템은 피에조 스택 액추에이터와 수동형 마운트가 커플링된 구조를 가지고 있다. 전체 시스템에 대한 동적 모델이 유도되고 각 경로의 스택 액추에이터 입력 힘과 위상이 각 경로의 완전한 절연을 타겟으로 하여 결정된다. 진동 저감 성능이 확인되고 이는 가장 좋은 저감을 가져오는 수동형 및 능동형 경로의 최적화된 결합을 제시한다.

• Smart Structures and Systems
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• 제26권5호
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• pp.657-666
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• 2020

A rotational pulse-echo ultrasonic propagation imager that can inspect cylindrical specimens for material nondestructive evaluations is proposed herein. In this system, a laser-generated ultrasonic bulk wave is used for inspection, which enables a clear visualization of subsurface defects with a precise reproduction of the damage shape and size. The ultrasonic waves are generated by a Q-switched laser that impinges on the outer surface of the specimen walls. The generated waves travel through the walls and their echo is detected by a Laser Doppler Vibrometer (LDV) at the same point. To obtain the optimal Signal-to-Noise Ratio (SNR) of the measured signal, the LDV requires the sensed surface to be at a right angle to the laser beam and at a predefined constant standoff distance from the laser head. For flat specimens, these constraints can be easily satisfied by performing a raster scan using a dual-axis linear stage. However, this arrangement cannot be used for cylindrical specimens owing to their curved nature. To inspect the cylindrical specimens, a circular scan technology is newly proposed for pulse-echo laser ultrasound. A rotational stage is coupled with a single-axis linear stage to inspect the desired area of the specimen. This system arrangement ensures that the standoff distance and beam incidence angle are maintained while the cylindrical specimen is being inspected. This enables the inspection of a curved specimen while maintaining the optimal SNR. The measurement result is displayed in parallel with the on-going inspection. The inspection data used in scanning are mapped from rotational coordinates to linear coordinates for visualization and post-processing of results. A graphical user interface software is implemented in C++ using a QT framework and controls all the individual blocks of the system and implements the necessary image processing, scan calculations, data acquisition, signal processing and result visualization.

• 한국정밀공학회지
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• 제23권5호
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• pp.37-43
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• 2006

Fitting process carried out in automobile transmission assembly line is classified into three classes; heat fitting, press fitting, and their combined fitting. Heat fitting is a method that heats gear to a suitable range under the tempering temperature and squeezes it toward the outer diameter of shaft. Its stress depends on the yield strength of gear. Press fitting is a method that generally squeezes gear toward that of shaft at room temperature by press. Another method heats warmly gear and safely squeezes it toward that of shaft. Warm shrink fitting process for automobile transmission part is now gradually increased, but the parts (shaft/gear) assembled by this process produced dimensional change in both outer diameter and profile of the gear. So that it may cause noise and vibration between gears. In order to solve these problems, we need an analysis of warm shrink fitting process, in which design parameters are involved; contact pressure according to fitting interference between outer diameter of shaft and inner diameter of gear, fitting temperature, and profile tolerance of gear. In this study, an closed form equation to predict contact pressure and fitting load was proposed in order to develop optimization technique of warm shrink fitting process and verified its reliability through the experimental results measured in the field and FEM, that is, thermal-structural coupled field analysis. Actual loads measured in the field have a good agreement with the results obtained by theoretical and finite element analysis and also the expanded amounts of the outer diameters of the gears have a good agreement with results.

• 한국항공우주학회지
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• 제33권9호
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• pp.89-96
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• 2005

이 논문에서는 주간 항법용 별센서의 실제 활용을 목적으로 주간 대기 조건과 주간 별 감지 가능성을 논한다. 주간동안의 대기 자료를 구하기 위해 표준 대기 모델(LOWTRAN 7)을 사용했으며 그 모델로부터 배경하늘에 대한 복사와 대기투과도를 구하였다. 대기 복사량을 감소시키기 위해 광학 필터를 장착한 별센서를 가정했으며 태양 복사 효과를 나타내기 위해 별센서와 태양 사이의 다양한 분리각을 설정하였다. 별센서의 FOV에 대한 고려로서, 하늘 배경 복사의 변화와 감지가능한 별의 개수 밀도를 분석하였다. 또한 요구되는 신호 대 잡음비를 얻기 위한 노출시간과 별센서의 주간 활용 한계로서 작용하는 CCD의 복사에 의한 전자 수를 계산하였다.

• 한국전자통신학회논문지
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• 제12권6호
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• pp.1065-1070
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• 2017

마그네틱 기어는 기계적인 접촉 없이 회전 기계의 입력측과 출력측이 자기적으로 결합되어 동력을 전달한다. 마그네틱 기어는 내측회전자, 외측회전자, 폴피스로 구성되어 있으며, 동력전달 시 두 회전체와 폴피스 사이의 자기저항 차이로 토크리플이 발생하게 된다. 이러한 토크리플은 회전기계의 소음과 진동의 원인이 되기 때문에 최소화하는 방안이 필요하다. 본 논문에서는 토크리플 저감 방안으로 폴피스의 각진 모서리를 깎아 필렛을 적용한 형상을 제안하였다. 2D 유한요소해석법을 활용하여 필렛 파라미터 변화에 따른 마그네틱 기어의 토크리플을 비교 및 분석하고 토크리플이 우수한 폴피스 형상을 모색하였다.